1. Field of the Invention
The present invention relates to a wireless LAN apparatus and a semiconductor device for achieving a step-by-step reduction/restoration of power.
2. Description of the Related Art
In recent years and continuing, the standardization of wireless LAN (Local Area Network) technology according to IEEE 802.11 (Institute of Electrical and Electronics Engineers 802.11) is growing. Such wireless LAN technology is introduced as an alternative of the conventional wired network technology or as a technology that is to coexist with the wired network technology. The functions of the wireless LAN technology are typically attained by employing a device such as a PC card that follow standards of organizations such as the PCMCIA (Personal Computer Memory Card International Association). The device, such as the PC card, is mainly used by being mounted in a personal computer. For the purpose of saving electrical power, the personal computer includes a function of switching off the power supply to various parts in the personal computer when the personal computer is not used for a predetermined period of time.
FIG. 1 is a schematic view of an exemplary configuration of a related art configuration for controlling the power of a wireless LAN function part. In FIG. 1, a PC card 200, which is mounted in a personal computer 100, includes integrated IC chips 201 and 204. The IC chip 201 includes a MAC processing part 202 for performing media access control (e.g. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) and a BB (Base Band) processing part 203 for processing BB (Base Band) signals. The IC chip 204 includes an RF (Radio Frequency) processing part for processing high frequency (RF: Radio Frequency) signals. In an operation of transmitting wireless signals from an antenna 206 of the PC card 200, transmission signals travel from a CPU 101 of the personal computer 100 to the antenna 206 via the MAC processing part 202, the BB processing part 203, and the RF processing part 205. In an operation of receiving wireless signals from the antenna 206, reception signals travel from the antenna 206 to the CPU 101 of the personal computer 100 via the RF processing part 205, the BB processing part 203, and the MAC processing part 202.
In an operation for switching off the power of a wireless LAN function part, a signal instructing to switch off the power is transmitted from the CPU 101 of the personal computer 100 to the IC chips 201 and 204 of the PC card 200 at a predetermined timing. In a case of restoring (reactivating) the power, a signal instructing to switch on the power is transmitted from the CPU 101 of the personal computer 100 to the IC chips 201 and 204 of the PC card 200 at a predetermined timing.
Owing to growing demands for increasing the functions of office apparatuses, the wireless LAN function is added not only to the personal computer, but also to office apparatuses such as printers and copy machines. The power of printers and copy machines more often tends to be kept in a continuously on-state compared to the power of the personal computer. Accordingly, there is a considerable demand for reducing the power consumption of office apparatuses such as printers and copy machines, and the demand for reducing the power consumption of the wireless LAN function part thereof is no exception. Furthermore, in a case where a personal computer is not being used, shutting down or switching to a sleep mode may not serve as a problem for the user. Meanwhile, it would be inconvenient to completely switch off the functions of printers and copy machines since a printing job, for example, may be ordered at any time via a network connected to the printers and copy machines.
In controlling the power of the conventional wireless LAN function part of the personal computer 100 shown in FIG. 1, the power of the PC card can only be switched off entirely and switched back on (restored), for example, by having the user perform a prescribed maneuver. Therefore, it is difficult to reduce the consumption of power for the wireless LAN function part.
In order to reduce power as much as possible while maintaining minimal necessary functions, it is possible to control the power for each module included in a wireless LAN apparatus. However, since the wireless LAN function part normally uses multiple clock signals, it is necessary to conceive a control procedure that is able to prevent the multiple clock signals from causing any errors. That is, the wireless LAN apparatus shown in FIG. 1 relies on clocks signals for two circuits (systems) in which one of the clock signals is used for the CPU 101 of the personal computer 100 and the other clock signals is used for the RF processing part 205, the BB processing part 203, and the MAC processing part 202. Therefore, it is desired to conceive a control procedure for reducing and restoring the power of each module while taking the multiple clock signals into consideration.